Manufacture of alloys of iron, chromium, nickel, and copper



oxide.

Patented Feb. 18, 1936 MANUFACTURE OF ALLOYS OF IRON, CHROMIUMfNICKEL, AND COPPER Alexander L. Feild, Baltimore, Md., assignor, by mesne assignments, to Rustlesslron and Steel Corporation of America, Baltimore, Md., a corporation of Delaware No Drawing. Application August 10, 1932,

Serial No. 628,185

13 Claims. (01. 15-45) The present invention relates to the manufacture of alloys of iron, chromium, nickel and. copper, and more particularly to an economical method for the manufacture of low-carbon corrosion-resistant nickel-chromium steels containing a substantial percentage of copper. The process is particularly applicable to the manufacture of the low-carbon steels commonly called rustless irons, in which the carbon content is usually in the neighborhood of .05 to .15%.

In producing the alloy, the nickel and copper content is derived primarily from a cheap source consisting of the calcined Sudbury ore containing nickel and copper which is employed as the source of the alloy known commercially as Monel metal and, containing approximately 2 parts by weight of nickel to 1 part of copper.

In the manufacture of Monel metal from the sulphide ores of the Sudbury district in the Province of Ontario, Canada, a matte is first produced containing about 25% copper, nickel and 20% sulphur. .This matte is calcined in an oxidizing atmosphere to eliminate the sulphur and convert the nickel and copper into their oxides. This product, which contains the oxides of the nickel and copper inthe natural proportions occurring in the ore is known as Monel This is the material which I prefer to employ in carrying out my process. It is now an intermediate product in the making of Monelmetal and can be obtained relatively cheaply. By using this product instead of Monel metal I materially decrease the cost of making my alloys of iron, chromium, nickel and copper. The nickel and copper oxides, moreover, serve a function in the process in reducing carbon to produce a lowcarbon steel.

The corrosion-resistant steel 'or alloy which I produce preferably contains a relatively high percentage of chromium, usually not less than about 10%, so as to impart a rustless or stainless character to the metal. The carbon content is preferably low, usually not more than about .10%. I prefer that the finished rustless iron or steel shall have a combined nickel and copper content of not less than about 8% or over 25%. I set the lower percentage of my preferred range at about 8% because a combined percentage of nickel and copper in this neighborhood is necessary to yield an austenitic steel when the chromium content is in the usual ranges of 16 to 19% for such austenitic steels. I set an upper limit of my preferred range at 25% for the combined percentage of nickel and copper because at a chromium range of 16 to 19% it is not readily possible to introduce more than this combined percentage of nickel and copper from Monel oxide without an appreciable sacrifice in economy of operation. I do not, however, limit myself to these preferred ranges. For example, the combined percentage of nickel and copper may below enough to yield a martensitic or ferritic steel instead of an austenitic steel.

According to my process, a suitable electric furnace, such, for example, as the usual Heroult steel-melting furnace, is given a charge consisting principally of low-carbon steel scrap which preferably consists, in part, of chromium-nickelcopper steel scrap of the same general analysis as that which is to be made; ordinary high-carbon ferrochrome containing, as a rule, from 4 'to 6% carbon; and a relatively large quantity of Mone1" oxide with or without the addition of a material high in iron oxide, such as roll scale or magnetic iron ore concentrate. The power is applied and the charge is-melted down forming a bath of ferrous metal and a supernatant oxidizing slag. The molten bath is brought to a relatively high temperature which is continued until the carbon content of the metal bath is at or below the predetermined maximum percentage. During this oxidizing period, a considerable quantity of chromium is oxidized along with the carbon by the oxides of copper, nickel and iron contained in the slag. The oxides of chromium enter the slag. At the same time all or a substantial proportion of the nickel oxide and copper oxide originally in the slag is reduced to metallic nickel and copper and enters the metal bath. When the carbon content of the metal bath has fallen to the desired low figure, the percentage of chromium in the bath is very substantially lower than that which is desired in the finished product, and, in general, is less than 10%.

The second stage of the operation consists in the addition of relatively large quantities of burnt lime and ferrosilicon, preferably crushed, to the bath. The silicon reacts with the reducible o'xides in the slag and enriches the bath in chromium up to the desired percentage without any increase in carbon content. In addition to chromium and iron, a certain small-percentage of nickel and copper may be also transferred to the metal bath from the slag, Recovery of the chromium, nickel and copper is practically complete and the final finishingv slag is of the well-known calcium silicate type.

As a specific example of my process, the following procedure employed for the manufacture of ingots containing 16 to 18% chromium, about 6% nickel, about 3% copper, and not more than .10% carbon, is described: 6,360 pounds of steel scrap, analyzing approximately 16 chromium, 6% nickel and 3% copper, and 5,000 pounds of ordinary low-carbon steel scrap, were first charged onto the bottom of a six-ton Heroult electric furnace. Along with the scrap was charged 2,500 pounds of lump high-carbon ferrochrome, analyzing approximately 5% carbon and chromium; 1,600 pounds of Monel oxide, analyzing approximately 40% nickel and 18% copper; and 2,000 pounds of roll scale, an alyzing about 69% iron. The electric power was applied the charge was melted down, and thereafter superheated to a degree suflicient to permit the charging of an additional 1,000 pounds of roll scale. The iron, nickel and copper oxides form an oxidizing slag. The temperature was maintained at superheat until a metal test showed .09% carbon. No reliable method is known to me for accurately determining the temperature of the metal bath under. the slag blanket, but it is estimated that this temperature should be approximately 3050 to 3200 R, which is some 100 to 250 F. higher than that usually employed in ordinary electric steel melting practice. The superheating of the bath to a temperature above that ordinarily employed in electric steel melting practice is preferred, since the; superheat renders the action of the iron, nickel and copper oxides more energetic in oxidizing the carbon from the metal;

Next, 1,450 pounds of crushed ferrosilicon and 3,300 pounds of burnt lime were added to the slag as rapidly as conditions permitted. The silicon reducing agent reacted with the reducible oxides contained in the slag forming metals, which gravitated into the bath of molten metal, and silicates, which remained in the slag overlying the bath. When the light green appearance of the slag indicated that its reducible oxide content was low, final additions of lump ferrosllicon and low-carbon ferro'manganese were made to the bath and the metal was poured. Ladle tests showed analysis of 16.2% chromium, .08% carbon, 6% nickel and 2.9% copper, together with manganese, silicon, phosphorous and sulphur in normal amounts. The product of the heat weighed approximately 17,000 pounds.

When the initial scrap charge used consists entirely of ordinary low-carbon steel scrap, instead of a mixture of ordinary scrap with chromium-nickel-copper scrap as shown in the above example, it is necessary to employ a considerably larger quantity of Monel oxide. For example, in such a case the roll scale was entirely omitted and replaced with an equal weight of Monel metal oxide,.and the product of a heat of similar weight analyzed approximately 10.5% nickel and 6% copper.

To secure an alloy containing the maximum percentages of nickel and copper and made in accordance with my process, the ordinary steel scrap and roll scale are dispensed with and an initial charge is used consisting of chromiumnickel-copper steel scrap, high carbon ferrochrome, and an oxidizing agent consisting entirely of Monel metal oxide. Following such procedure an alloy containing approximately 17% nickel and 8% copper was produced:

In my process I employ a cheap source, not only of nickel and copper, but also a cheap source of chromium. namely, high-carbon ferrochrome.

Moreover, by virtue of the energetic oxidizing nature of the nickel and copper oxides, my process makes possiblethe efficient and cheap removal of carbon from the high-carbon ferrochrome employed. In other words, my process represents an unusual case where two cheap sources of alloying elements, one a natural mixture of oxides and the other a high-carbon ferro alloy, are

portions naturally occurring in the ore, on account of its cheapness and because the proportions of nickel and copper are suitable in most cases to supplement the chromium in securing stainlessness and rust-resistance, and obtaining, when desired, an austenitic steel, other sources of nickel and copper may be employed, with different proportions of the nickel and copper oxide if desired, as, for example, a mixture of nickel and copper oxides, or Monel oxide modified by the addition to it of other nickel or copper oxides. While I prefer to use as a reducing agent a ferrosilicon having a relatively high proportion of silicon, such as 75% ferrosilicon, other grades of ferrosilicon may be used or even silicon metal. Also, other exothermic reducing, agents may be employed, such as aluminum, magnesium, etc.

While the product obtained is preferably a low-carbon stainless or rustless steel of the type ordinarily called stainless or rustless iron, the process can be employed in the manufacture of stainless or rustless steels containing higher percentages of carbon.

The preferred product is an austenitic steel containing chromium from 10 to 20%, prefererably 16 to 19% of chromlum,.and from 8 to 25% combined nickel and copper, preferably 8 to 12% combined nickel and copper, in the proportions of approximately 2 parts of nickel and 1 part of copper. is preferably low, about .05% to .l5%, giving a metal that is especially resistant to corrosion, that readily lends itself to forming operations such as hot or cold rolling, deep-drawing, and the like, and which is comparatively free from carbide precipitation after severe heating and is thus free from intergranular attack upon being subsequently exposed to corrosive media. The steel may be made, however, containing other proportions of chromium, nickel and copper, such as 15 to 20% chromium,-or even 10 to 30% chromium; 6 to 14% nickel, or even 5 to 18%.

nickel; and 3 to 7% copper, or even 2 to 8% copper, the balance being principally'iron. v In general irons and steels of the higher chromium contents require the higher percentages of nickel and copper in order to produce an austenitic alloy, and, similarly, lower chromium contents permit lower amounts of nickel and copper; the proportion of nickel to copper, however, as indicated above, is preferably maintained in the ratio of about 2 to 1.

Since, for reasons of efllciency'and economy, a silicon-containing reducing agent is preferably employed in the practice of my process in the matter of reducing the oxides contained in the ination o: the metal. In order that a readily The carbon content of the iron or steel formable. metal which lends itself to an ease of heat treatment may be consistently produced the silicon content of the metal iskeptto a low value, in spite of the tendency toward silicon contamination where a high recovery of the oxides from. the slag is desired, by the exercise of care in making the ferro-silicon additions during the re-'-' ducing stage of the process. By this means the silicon content may be maintained under 1.00%. Minor proportions of otheralloying elements may be employed, such as manganese, vanadium, titanium, cobalt, tungsten, molybdenum, etc either singly or in combination. These additional alloying elements may be incorporated in the metal bath during the steel-making operation in accordance with well-known methods.

The copperapparently supplements the nickel in imparting certain desirable characteristics to a high chromium. steel, such as remarkable resistance to corrosion. g

While I have described the preferred embodiment of my invention, it is to be understood that the invention may be otherwise practiced within the scope of the following claims.

I claim: 1'. The process of making low-carbon ironchromium-nickel alloys, which comprises charging a furnace with low-carbon steel scrap, high carbon ferrochromium and "Monel" oxide, and heating. the charge to a temperature suflicient to fuse the scrap and form a supernatant layer of molten slag and to cause a reduction of. nickel and copper from their oxides to the metallic state.

accompanied by the oxidation of the carbon in the bath, thereafter adding to the slag a silicon reducing agent and lime to reduce chromium together with residual nickel and chromium from their oxides in the slag.

2. The process of making low-carbon ironchromium nickel alloys, which comprises charging a furnace with low-carbon steel scrap, highcarbon ferrochromium and Monel oxide, and.

heating the charge'to a temperature sufficient to fuse the scrap and form a supernatant layer of.

molten slag and to cause a. reduction of nickel and copper from their oxides to the metallic state accompanied by the oxidation of the caricon in the bath, thereafter adding to the slag a silicon reducing agent to' reduce chromium together with residual nickel and chromium from their oxides in the slag.

3. The process of making iron-chromiumnickel-copper alloys, which comprises heating in a furnace a charge containing iron scrap, highcarbon ferrochromium and nickel and copper oxides to a temperature sufiicient to fuse the scrap and form a supernatant layer of molten slag and cause a reduction of nickel and copper.

to the metallic state, andthereafter adding an exothermic reducing agent to the slag to reduce the oxides in the'slag to a metallic state.

4. The process of making low-carbon chromiiun-nickel-copper rustless steel, which comprises melting in an electric furnace steel scrap, high-carbon ferrochromium, and nickel and copper oxides so as to fuse the scrap, reduce metallic nickel and copper from their oxides and oxidize carbon from the charge, and form a supernatant layer of molten slag containing chromium oxide, and thereafter adding to the bath a suitable reducing agent and.lime to reduce the chromium from the slag back into the metal.

. 5. The process of making low-carbon chromium-nickel-copper rustless steel, which comprises melting in an electric furnace steel scrap,

2,031,321 Y 3 ,high-carbon ferrochromium, and Monel" oxide so as to fuse the scrap, reducemetallic nickel and copper from their oxides and oxidize carbon from the charge, and form a supernatant layer of molten slag containing chromium oxide, and thereafter adding to the bath a suitable reducing agent and lime to reduce thechromium from the slag back into the metal.

- metal of low-carbon content containing chromium, nickel and copper.

7'. That step in theprocess of making low-carbon'nickel-copper rustless steel in an electric arc furnace, whichconsists in melting in said furnace a charge containing steel scrap, high-carbon ferro-chromium and Monel" oxide to'a temperature sufficient to fuse the scrap, oxidize the greater part of the carbon and cause a reduction ofnickel andcopper, whereby a low-carbon chromium-iron alloy containing metallic nickel and copper is-produced. i

8. In the productionof rustless iron containing nickel and copper, the art which includes. reducing oxides of nickel and copper with .highcarbon ferrochromium in the presence of molten ferrous metal, forming thereby a bath of ferrous metal low in carbon-and containing chromium, copper and nickel.

9. In the production 'of a low-carbon ferrous alloy containing chromium, nickel and copper,

, the art whichincludes, preparing a ferrous metal bath containing chromium covered by a blanketof slag rich in the oxides of chromium, nickel and copper, and reducing the metallic oxides contained in the slag with a silicon reducing agent, therebyenriching the bath in the metals, chromium, nickel and copper.

10. In the production of rustless iron containing nickel and copper, the art which includes, preparing a low-carbon ferrous metal bath containing chromium and an overlying blanket of slag rich in the oxides of chromium, nickel and copper, and reducing the metallic oxides contained in the slag with a non-carbonaceous reducing agent, thereby enriching the bath in the metals, chromium, nickel and copper.

11. In the production 'of low-carbon iron-' chromium-nickel-copper alloys in an electric arc furnace, the art which includes, melting down in said furnace acharge including high carbon ferrochrome, and copper and nickel oxides, forming thereby abath of ferrous metal containing chrocopper. and nickel with a supernatant slag containing oxides of copper and nickel; and thereafter reducing the oxides present in the slag to effect a recovery of their metallic values and an enrichment of the bath in the metals copper -and nickel.

.12. In the production in an electric arc furnace of low-carbon rustless steel containing copper and nickel, the art which includes, melting down in said furnace rustless iron or steel scrap, high-carbon ferrochrome, copper and nickel oxides, and an oxide of iron, forming thereby a low-carbon bath of ferrous metal containing chromium and a supernatant slag containing the oxides of chromium, copper and nickel; and

to achieve a recovery of their metallic values and an enrichment of the bath in th metals chromium, copper 'and nickel.

13. In the production of low-carbon ironohromium-nickei-copper alloys in an electric arc furnace. the art which includes, ioi-ming in said furnace a low-carbon-bath of ferrous metal contaming chromium with a supernatant slag con-- taining the oxides of chromium, copper and nickel; and thereafter reducing the oxides present in the slag under basic conditions and emplaying a non-carbonaceous reducing agent to effect a recovery of the metallic values in the slag and an enrichment of the bath in the metals chromium, copper and nickel.

a ALEXANDER L. FEILD.

CERTIFICATE OF CORRECTION.

Patent No. 2,031,152. February 18, 1936.

ALEXANDER L. FEILD.

It is hereby certified that the name of the assignee in the above numbered patent was erroneously written and printed as "Rustless Iron and Steel Corporation of America" whereas said name should have been written and printed as Rustless Iron and Steel Corporation, as shown by the records of assignments in this office; and that the saidLetters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. Signed and sealed this 31st day of March, A. D. 1936.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

